buying a house

[JohnW2]

Exactly, and what floor area would that cover?

Well, if it were the one and only socket in a 100m² room, it would 'cover' 100m² - but that obviously illustrates the silliness of this attempt at a guideline.

Incidentally, why does this spurious limit NOT apply to socket radial circuits?

It does - see Fig 15B in Appendix 15 - 'historically' 50m² for a 20A radial and 75m² for a 32A one.

As for the OSG, unless I'm missing it, my (red) one seems not to mention floor areas. However, what it does do is offer guidance relating the the minimum number of socket outlets in each type of room (Table 8B in mine)!

Whilst we are talking about 'interesting' bits of guidance in the OSG (whose section about "Socket-outlet Circuits" does not seem to recognise anything other than ring finals), how about ...

As a rule of thumb for rings, unfused spur length should not exceed 1/8 of the cable length from the spur to the furthest point on the ring.

Kind Regards, John

 

[EFLImpudence]

It does - see Fig 15B in Appendix 15 - 'historically' 50m² for a 20A radial and 75m² for a 32A one.

Yes, but why is it different for 32A circuit - if concerned with loading?

As for the OSG, unless I'm missing it, my (red) one seems not to mention floor areas. However, what it does do is offer guidance relating the the minimum number of socket outlets in each type of room (Table 8B in mine)!

I don't have any OSGs.

Whilst we are talking about 'interesting' bits of guidance in the OSG (whose section about "Socket-outlet Circuits" does not seem to recognise anything other than ring finals), how about ...

No idea. It really is not good enough.

 

[JohnW2]

Yes, but why is it different for 32A circuit - if concerned with loading?

That's surely clear enough, even if it is pretty useless - they are attempting to estimate likely electricity requirements on the basis of the size of the room(s) being supplied by the circuit. However, that is such an imprecise guide as to be, in practical terms, pretty useless. In the absence of electrical heating, a 15m² kitchen/utility room would be likely to need a lot more electricity than a 50m² dining room!

No idea. It really is not good enough.

Quite so. Try as I may, I find it difficult to imagine what they could have been thinking of when they wrote that one! Provided only that it satisfied requirements/guidelines in relation to Zs and VD, an unfused spur could surely be as long as it liked/wanted?

Kind Regards, John

 

[John D v2.0]

they are attempting to estimate likely electricity requirements on the basis of the size of the room(s) being supplied by the circuit

Given average insulation levels, unless you're growing cannabis, if you're using more power than that you're probably going to have to open windows even in the middle of winter!

 

[JohnW2]

Given average insulation levels, unless you're growing cannabis, if you're using more power than that you're probably going to have to open windows even in the middle of winter!

IT's the "that" of "...more power than that" which is impossible to sensibly estimate on the basis of floor area alone.

As I've said, X m² of, say, kitchens, utility rooms or workshops is likely to represent a much higher electricity load than is X m² of, say, reception rooms, bedrooms, store rooms etc. ... and, furthermore, an 3X m² utility room is most unlikely to use three times more electricity than an X m² one.

As EFLI pointed out at the start, floor area alone is essentially useless as an estimator of electricity usage.

Kind Regards, John

 

[lanswerted]

can an installation be deemed safe with a set number of sockets but not fit for purpose when wanting to add kitchen lights under units or items such ad a tower rail
basically if a pass certificate is shoved under my nose does that mean that within reason other items could be added to this 1970s wiring?

 

[terryplumb]

Any inspection / certification now has no bearing on what additions you intend to do in the future.

 

[JohnW2]

can an installation be deemed safe with a set number of sockets but not fit for purpose when wanting to add kitchen lights under units or items such ad a tower rail .... basically if a pass certificate is shoved under my nose does that mean that within reason other items could be added to this 1970s wiring?

If the installation is "deemed to be safe" (which means "safe", not necessarily "fit for purpose"), certificate or no certificate, then anything can be added, provided it is done appropriately, correctly and competently (with appropriate testing after the additions).

Kind Regards, John

 

[securespark]

Yes, but why is it different for 32A circuit - if concerned with loading?

Dunno for sure, but:

H2 Final circuits using socket outlets complying with BS1363-2 and fused connection units complying with BS1363-4

H2.1 General
In this arrangement, a ring or radial circuit, with spurs if any, feeds permanently connected equipment and a number of socket outlets and fused connection units.

The floor area served by the circuit is determined by the known or estimated load and should not exceed the value given in Table H2.1

 

[EFLImpudence]

Please don't quote the OSG as it has no authority and frequently varies from BS7671 because it states worst-case scenarios to save those using it having to work out anything.

E.g. tails must be a minimum of 25mm².

 

[JohnW2]

Dunno for sure, but:

Your green OSG is obviously very different from my red one. Mine has numbered (not 'lettered') sections and Tables, and I can see nothing equivalent to the material you've quoted in mine.

Since your green one 'out-ranks' my red one, I don't thin k I can usefully/safely add any more.

Anyway, regardless of what any OSG might say, can we not agree that to base the design on any circuit on 'floor area supplied' alone is a total nonsense?

Kind Regards, John

 

[ban-all-sheds]

Please don't quote the OSG ...

Please don't keep pretending that you don't know the difference between "should" and "must".

 

[EFLImpudence]

Sorry. I don't have a copy. I remembered wrongly - justifiably.

If it says "should be a minimum of 25mm²" that is even worse.

 

[ban-all-sheds]

I was referring to your objection to this:

The floor area served by the circuit is determined by the known or estimated load and should not exceed the value given in Table H2.1

not your comment on tails.

 

[securespark]

Since your green one 'out-ranks' my red one, I don't think I can usefully/safely add any more.

John, the Appendices were "re-numbered", using letters instead. Appx 8 became Appx H.